Method for verifying tires of vehicles in the driving state

ABSTRACT

In a method for checking tires of vehicles during driving, signals which provide information about an adhesion between the tire and the roadway in the vertical direction with respect to the roadway are detected by sensors provided at the tire. The signals are evaluated in an evaluation unit with respect to their amplitude, such that the amplitude characteristic for the detected signals can indicate a disturbance occurring at the tire. An occurrence of a disturbance is indicated on a display unit and is stored for diagnostic purposes.

FIELD OF THE INVENTION

The present invention relates to a method for checking vehicle tiresduring driving.

BACKGROUND INFORMATION

It is of utmost importance for driving safety that the tires of a motorvehicle be in good condition. Generally the tires are examined byappearance for their further future operational fitness during theirseasonal change from summer to winter tires, and then are possiblyexchanged for new tires. However, the tires are not always balanced whenbeing changed. The result is that an imbalance appearing at the tire canimpair driving safety. It can also occur that the operational fitness ofa tire on a vehicle is impaired because of a braking which is too strongor from standing too long in one position; this impairment can possiblybe rectified by balancing the tires.

From Stöcker, Jörg, i.a.: Der “Intelligente Reifen”—Zwischenergebnisseeiner interdisziplinären Forschungskooperation [The “IntelligentTire”—Intermediate Results of an Inter-disciplinary ResearchCooperation] in ATZ Automobiltechnische Zeitschrift 97, 1995, 12, P.824-832, it is known to equip a tire with an integrated force sensor bywhich it is possible to detect forces acting upon the tire in threedirections, namely, the longitudinal or X direction, the transverse or Ydirection and the vertical or Z direction. The signals derived fromthese detected forces can be supplied to an evaluation unit in which adesired evaluation of the signals is carried out.

The German Published Patent Application No. 196 20 581 describes afurther device for ascertaining the rotational behavior of a vehiclewheel.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for checkingvehicle tires during driving, by which a disturbance occurring at thetire can be detected.

The design approach of the present invention utilizes a signal detectedby a tire sensor for determining a disturbance occurring at the tire,the amplitude characteristic of the signal being analyzed during onewheel revolution. The amplitude characteristic for the detected signalis advantageously analyzed repeatedly for a number of periods, oneperiod corresponding to one wheel revolution. Furthermore, the analyzedamplitude characteristic can be compared to the amplitude characteristicof a signal produced by a sensor at another tire in order to giveplausibility to the test results. The appearance of a disturbance at thetire, e.g. a tire imbalance, can be indicated by a display unit. Thedisplay unit can also then indicate advice and recommendations for thedriver. In addition, upon detection of a disturbance at the tire, asignal can be supplied to the engine management in order to influenceit.

The method of the present invention makes it possible in particular todetect a disturbance or a defect at a tire of a vehicle, for example, atire imbalance, while driving. A vehicle driver can thereby reliablydetermine himself whether tires on his vehicle must be changed orbalanced, since it can be indicated to him by a display unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a system for carrying out the method ofthe present invention for checking the behavior of vehicles duringtravel operation.

FIG. 2 shows a schematic flow chart of one possibility for determining adisturbance at the tire of a vehicle.

FIG. 3 shows a schematic flow chart of a further possibility fordetermining a disturbance at the tire of a vehicle.

FIG. 4 shows a schematic flow chart of another possibility fordetermining a disturbance at the tire of a vehicle.

DETAILED DESCRIPTION

According to FIG. 1, using a sensor 10 provided at the tire, signals aredetected during driving which provide information about the adhesionbetween the roadway and the tire. Signals can be detected in the Xdirection in the direction of travel or contrary to the direction oftravel of the tire, in the Y direction transverse to the direction oftravel of the tire, or in the Z direction vertical to the direction oftravel. The signals in the Z direction of interest here describe theradial adhesion between the roadway and the tire. Examples for signalsin the Z direction can be gathered, for example, from pictures 13 and 14in the article by Stöcker, Jörg, i.a. indicated above: Der “IntelligenteReifen”—Zwischenergebnisse einer interdisziplinärenForschungskooperation in ATZ Automobiltechnische Zeitschrift 97, 1995,12, P. 824-832.

The signals in the Z direction have a uniform characteristic with theperiod of the rotational speed of a tire. The amplitudes of the signalsvary, for example, as a function of the tire internal pressure, whichcan thus be measured by the system described in the article by Stöcker,Jörg, i.a.: Der “Intelligente Reifen”—Zwischenergebnisse einerinterdisziplinären Forschungskooperation in ATZ AutomobiltechnischeZeitschrift 97, 1995, 12, P. 824-832.

Prerequisite for such a measurement is that the tire is running trueduring driving and is not influenced by any disturbances. If themeasurement is carried out at a tire which, because the vehicle has beeleft standing too long or because of too strong a braking, has a flatspot, i.e. a “flat foot”, or which is no longer properly balanced, thenthe signals measured during driving no longer exhibit the periodicallyrecurrent, normal amplitude characteristic. Instead, because of anout-of-round location on the tire, a disturbance appears in theamplitude characteristic which, for example, can be recognized in theform of a peak or peak value, or by a deviation from the even amplitudecharacteristic.

To determine whether the amplitude characteristic of the signal detectedduring driving by a tire sensor 10 has a disturbance or not, thedetected signal is supplied to an evaluation unit 20 shown in FIG. 1. Inevaluation unit 20, it is then checked whether the signal was detectedin an error-free manner. In addition, the detected signals are subjectedto a filtering. An adjustment, described in detail later, and a query ofa counter to be implemented in the further course of the method are alsocarried out. These individual steps are preferably run through prior toa further processing of the detected signals, as is indicated in FIGS. 2through 4. After determining the amplitude of the detected signals,evaluation unit 20 can then establish in various ways whether adisturbance exists at the tire.

The evaluation unit can carry out a comparison with characteristiccurves, stored previously in a memory, with tolerance band for thenormal operation. This requires a previous knowledge about parameters ofthe tire, such as the tire internal pressure, for which differentcharacteristic curves are valid. This possibility for determining adisturbance at the tire of a vehicle is shown schematically in FIG. 2.

A further possibility for determining a disturbance at the tire of avehicle in evaluation unit 20 is to analyze the amplitude characteristicof a detected signal for sudden changes. This can be done, for example,by continuously comparing an acquired amplitude value to an amplitudevalue acquired directly before that. If, in so doing, the differencebetween the compared amplitude values is greater than a predeterminedvalue, then a sudden (amplitude) change is determined. This possibilityfor determining a disturbance at the tire of a vehicle is shownschematically in FIG. 3.

Furthermore, evaluation unit 20 can be designed in such a way thatsignals SO and SI detected at two or more tires of a vehicle aresupplied to it simultaneously. These signals S0 and S1 are then comparedto one another. If the comparison shows that the amplitudecharacteristics of detected signals S0 and S1 are equal to one another,no tire disturbance exists. Otherwise, a tire disturbance can beassumed. When working with this possibility for detecting a disturbanceat the tire of a vehicle, it is presupposed that the tire at whichcomparison signal S1 is detected has no disturbance. This possibilityfor determining a disturbance at the tire of a vehicle is shownschematically in FIG. 4.

The last indicated comparison of the amplitude characteristic of asignal detected at one tire to an amplitude characteristic of a signaldetected at another tire can also be carried out in addition to the twopossibilities for analyzing the amplitude characteristics of detectedsignals first indicated, in order to give plausibility to the respectivetest results. The other tire can be arranged in the axle direction, intransverse direction or in diagonal direction with respect to the tirejust checked.

To ensure that a sudden change in amplitude, i.e. an amplitude deviationor difference of a detected signal actually results from a tiredisturbance and not from a disturbance on the roadway such as holes orstones on the roadway, provision is made to carry out the analysis overseveral periods. This can be implemented by setting a counter to amaximum number of periods corresponding to the number of revolutions ofa tire, for which number the analysis is to continue. An increment takesplace after each analysis, until the set maximum number of periods isreached. Only after the counter has expired is it decided—if the suddenchange in amplitude, that is to say the amplitude deviation ordifference of a detected signal has occurred in each of the countedperiods—that a disturbance exists at the tire.

The existence of the disturbance at the tire can be brought to theattention of a driver via a display unit 30 shown in FIG. 1. The displaycan be such that a behavior of the vehicle, for example, banging orvibrations, is explained to the driver. Furthermore, a specific speedcan be recommended which is suitable for eliminating the unpleasanttravel feeling for the driver. The engine management can also limit thespeed. In addition, a diagnostic entry for the service station can bewritten into a memory.

The vehicle condition is indicated to the driver by the detection of atire imbalance according to the present invention. This is particularlyimportant in the case of rental vehicles and company vehicles whosedrivers change frequently. The detection of a tire imbalance increasesdriving safety.

What is claimed is:
 1. A method for checking a behavior of a vehicleduring driving, comprising: causing sensors provided at a tire to detectsignals providing information about an adhesion between the tire and aroadway in a vertical direction with respect to the roadway; comparing,in an evaluation unit, amplitude characteristics of the detected signalsto a selected one of a plurality of different characteristic curves ofthe tire; and determining a disturbance occurring at the tire based onthe comparison.
 2. The method according to claim 1, further comprising:comparing in the evaluation unit the amplitude characteristics of thedetected signals to a previously stored amplitude characteristic curvefor a normal state of the tire in order to determine an amplitudedeviation.
 3. The method according to claim 1, further comprising:comparing in the evaluation unit an amplitude of one of the detectedsignals to an amplitude of another signal detected directly before theone of the detected signals, in order to determine a sudden change inamplitude.
 4. The method according to claim 1, further comprising:comparing in the evaluation unit an amplitude of one of the detectedsignals to an amplitude of another signal detected by another sensor atanother tire, in order to determine an amplitude difference between theone of the detected signals and the detected other signal.
 5. The methodaccording to claim 1, further comprising: in the evaluation unit,comparing the amplitude characteristics of the detected signals toamplitude characteristic of other signals detected at at least one othertire.
 6. The method according to claim 1, further comprising: evaluatingthe amplitude characteristics of the detected signals, and performingthe comparing for a predetermined number of periods corresponding to anumber of revolutions of the tire.
 7. The method according to claim 6,wherein: the predetermined number of periods is set in a counter.
 8. Themethod according to claim 1, further comprising a performance of atleast one of the steps of: causing a display unit to indicate thedisturbance to a driver; and supplying a signal indicative of thedisturbance to an engine management to possibly influence the enginemanagement.
 9. The method according to claim 8, wherein: the displayunit indicates a recommendation for a further driving to the driver. 10.The method according to claim 1, further comprising the step of: upondetermining the disturbance at the tire, storing a diagnostic entry fora service station in a memory.
 11. The method according to claim 1,wherein each of the plurality of different characteristic curvescorresponds to a different tire internal pressure.